Punch machine for punching electrical heater elements



Feb. 27, w51 J. GYURls 2,543,527

PUNCH MACHINE FOR PUNCHING ELECTRICAL HEATER ELEMENTS Filed Nov. l, 19463 Sheets-Sheet l umidi.

INVENTOR Jahn guns N'- J BY l `50 @l-M 57 53 ATTO RNEY Feb. 27, 1951 J.GYURIS 2,543,527

PUNCH MACHINE FOR PUNCHING ELECTRICAL HEATER ELEMENTS Filed NOV. l, 1946v Sheets-Sheet 2 FITTORNEY 25 3 j@ ji 2g 5g 55 Feb. 27, 1951 J. GYuRls2,543,527

PUNCH MACHINE FOR PUNCHING ELECTRICAL HEATER ELEMENTS Filed Nov. l, 19465 Shees--Shee'rI 5 lNvENToR Jan [Walvis HTTORNEY Patented Feb. 27, 1951PUNCH MACHINE FOR PUNCHING ELECTRICAL HEATER ELEMENTS John Gym-is, NewYork, N. Y.

Application November 1, 1946, Serial No. 707,106

16 Claims.

This invention relates to a heating element adapted for use in anelectric iron or other electrical appliance and to a method for makingsuch a heating element.

This invention further relates to a terminal construction which isparticularly adapted to make contact with a iiat, conductive portion ofa heating element.

This invention has further reference to a die constructed and arrangedto form a heating element in a single operation and to a method formaking the same.

This invention also embraces the construction of an electric iron orappliance embodying the novel heating element or terminal structure,alone or in combination.

Heretofore, heating elements for electric irons and other electricalappliances have ordinarily consisted of a ribbon or spiral of resistivematerial embedded in a mass of insulating material, this element beingsecured between two metal plates constituting the body of the iron.Aside from the inherent difficulties of constructing and assembling sucha structure, the prime disadvantage of this type of heating elementresides in the poor heat conduction between the heating element and thebody of the iron. This arises from the thickness of the insulatingmaterial which is necessary to enclose a spiral or ribbon of resistancematerial and adequately insulate it from the body of the iron, suchinsulating materials normally being poor conductors of heat. As aresult, the heating element is ordinarily operated at a temperature ofseveral hun-- dred degrees above the operating temperature of e theiron, resulting in rapid deterioration of the heating element andformation of an oxide lm thereon which is in itself a poor heatconductor, thus causing a further increase in the temperaturedifferential between the heating element and the body of the iron.

It has been proposed to substantially minimize this temperaturediierential by utilizing a substantially flat heating element in which anumber of slots are punched to deiine the respective segments of aheating element. However, difculties have been encountered with suchstructures in that it is extremely diflicult to provide an element withsuiiicient rigidity and mechanical strength to prevent buckling and thecontacting of adjacent resistance segments. In addition, diiiiculty isalso experienced in the manufacture of such elements in that a largenumber of closely-spaced slots must be formed in the heating element,usually by cutting one slot at a time, with the result that the processis quite expensive and diicult to perform.

In accordance with my invention, a heating element is provided in whichboth the resistance portions andthe terminal portions lie in a singleplane and in which the resistance portions are bonded to a sheet of heatresistant insulating material to provide the requisite mechanicalstrength and rigidity. In manufacturing my novel heating element, gridlike resistance elements are formed by suitable cutting or etchingoperations from a thin plate of resistance metal. The resistanceelements are interconnected, during the initial stages of the process,by portions of the plate of suicient size to provide enough mechanicalstrength and rigidity to prevent buckling. While in this stage, theresistance elements are bonded to a thin'sheet of heat resistantinsulating material, such as, for example, mica, to positively retainthe respective segments of the resistance element in their properrelation. Thereafter, the interconnecting portions are severed toprovide a resistance element bonded to the sheet of insulating materialwith at platelike terminal members extending from the respective endsthereof. I may then complete the resistance unit by bonding a secondinsulating sheet to the exposed surface of the plate.

In this manner, I eliminate the diiliculties arising from an excessivetemperature differential between the heating element and the metalplates associated therewith. This is explicable on the basis that myheating element is entirely flat throughout and free from buckling sothat it may be placed in intimate contact with the adjacent metalplates, separated therefrom only by extremely thin sheets of heatresistant insulating material. The advantages resulting from the use ofsuch thin sheets of insulating material may be better understood byreference to the following tabulation which compares the temperaturediierential Wi'th the thickness of the interposed insulating materialwhere the operating temperature is maintained constant at 250 C.

Temperature Thickness of Differential insulating Temperature betweenMaterial of Heating Heating (Mica) in Element Element Inches and Body ofIron C. C'. 0. 001 251 l 0.002 253 3 0.003 256 6 0.004 263 13 0.005 27525 0. 006 296 46 0.007 328 78 0.008 375 0` 009 436 186 0. 010 494 2440.011 547 297 0.012 598 348 0.013 648 398 0.014 696 446 0.015 742 4920.016 787 537 Conventional heating elements utilize insulating platesranging from about 0.013 inch to about 0.016 inch in thicknes and thetemperature differential, which is an index of the heat transferefficiency between the heating element and the iron, varies from about400 C. to about 550 C. It will be observed that the heating elements ofsuch irons are operated at temperatures on the order of 550 C. to '787C. which approaches red heat for Nichrome wire. This results in rapiddeterioration and oxidation of the heater structure. When the novelheating elements of this invention are utilized, the thickness of theinsulating material may be reduced to a thickness in the range from0.001 inch to 0.010 inch with a temperature differential of as little as1 to 244 C. Preferably, I utilize insulating material having a thicknessof 0.004 inch to 0.005 inch with a temperature diflerential of 13 C. to25 C. It will be noted that the element may be operated, in accordancewith the invention, at temperatures of about 250 C. to 300 C. which isinsufficient to cause deterioration or excessive oxidation of the heaterelement even when it is used for eX- tended periods. I have verifiedthese facts by extensive life tests and found that the novel heatingelements of this invention, after prolonged operation, show no signs ofdeterioration and preserve a bright untarnished surface. These resultsmay be attributed to the fact that the heater element is under theprotection of the heated body as a result of the intimate heat exchangerelation therebetween.

Another factor contributing to the low temperature differential andincreased emciency of my heating units is the novel terminalconstruction therefor. By the use of this structure, the terminalportions of the heating element may consist of plate-like membersintegrally formed with and lying in the same plane as the grid-likeresistance structure. I have found that the use of such terminalportions contributes substantially to the low temperature differentialof the heating element and I have devised a terminal structure formaking efficient contact with such fiat plate-like terminal members.

Another aspect of the invention relates to an improved die for forming,at a single operation, one or more rows of slots in a metal platedeiining grid-like resistance portions and terminals. With this die, alarge number of extremely thin, accurately positioned slots may beformed in a single operation and, in order to accomplish this result, Iprovide a plurality of die members each comprising a row of stackedmetal plates with corresponding plates in each row being of identicalthickness and having accurately aligned slots therein for receiving andguiding a cutting tool.

I prefer to make the respective sets of corresponding plates by placingthe plate portions of each set in side by side position, machining theplates to uniform thickness and forming aligned transverse slots in theplates while they are in such side by side position. Thereafter, Iassemble the plates in rows to form a plurality of die members with theplates of each set occupying corresponding positions in the respectiverows.

In view of the foregoing discussion, it will be seen that I haveprovided an eiicacious solution to many of the problems confronting themanufacturer of electrical appliances, such as electric irons andheating units.

It is an object of this invention to improve the construction andoperation of heating elements.

It is a further object of the invention to set forth a novel method ofmaking a heating element.

It is a still further object of the invention to provide an improvedterminal structure for a heating element.

The invention further aims to provide an electrical appliance, such asan iron, embodying the novel heating element from a plate of resistancemetal in a single punching operation.

It is another object of the invention to describe an improved method formaking such a die.

Other objects of the invention will be apparent from the followingdescription and accompanying drawings taken in connection with theappended claims.

The invention accordingly comprises the features of construction,combination of elements, arrangement of parts, and method of manufacturereferred to above or which will be brought out and exemplified in thedisclosure hereinafter set forth, including the illustrations in thedrawings, the scope of the invention being indicated in the appendedclaims.

For a fuller understanding of the nature and objects of the invention aswell as for specic fulfillment thereof, reference should be had to thefollowing detailed description taken in connection with the accompanyingdrawing, in which:

Figure 1 is a perspective view of an electric iron embodying the novelheater element and terminal structure;

Figure 2 is plan view showing a metal plate prepared for an etchingoperation;

Figure 3 is an end view of the plate shown in Figure 2;

Figure 4 is a plan view cf a metal plate having a series of slots formedtherein by a punching or etching operation;

Figures 5 and 6 are plan views of a partially completed heating element;

Figure '7 is a plan view illustrating the resistance unit bonded to asheet of heat resistant insulating material;

Figure 8 is a sectional view taken along the line 8-8 of Figure '7;

Figure 9 is a fragmentary perspective view of the completed resistanceunit;

Figure 10 is a plan view of a completed heating element of modiedstructure;

Figure 11 is a vertical sectional view of the novel terminalconstruction;

Figure 12 is a front elevational view, partially in section, of a dieconstructed in accordance with this invention;

Figure 13 is a side elevational view of the die shown in Figure 12;

Figure 14 is a plan View of the stationary die assembly;

Figure l5 is a sectional view taken along the line |5-i 5 of Figure 14;

Figure 16 is a perspective view showing a step in making the die ofFigure 12;

Figure 17 is a sectional View which is descriptive of another step inmaking the die of Figure 12; and

Figure 18 is a front elevational view showing a modification of the stepillustrated by Figure 17.

In each gure, the size of the slots shown therein is greatly exaggeratedfor clarity.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the construction of parts without 'departing from thespirit of the invention. In the following description and in the claims,parts will be identified by specific names for convenience, but they areintended to be as generic in their application to similar parts as theart will permit.

Referring now to the drawings in detail, Figures 2 to 9 illustratesuccessive steps in the method of making my novel heating element. InFigure 4, a thin plate I@ of resistance metal, such as Nichrome, isshown having two rows of slots A, B formed therein in the manner to behereinafter explained. Each row comprises a series of parallel, closelyspaced slots which are arranged in staggered formation so that each slotis laterally offset from the two slots adjacent thereto. Accordingly,each row may be said to consist of a group of slots II, the inner endsof which define the inner edge of a grid-like resistance element I2,Figure 6, together with a group of slots I3, laterally offset from slotsII, the outer ends of which define the outer edge of grid-likeresistance element I2.

It will be observed that the outer ends of the respective groups ofslots I3 denne substantially the outline of an electric iron, the slotsbeing shorter and more closely spaced adjacent the tip portion I2 thanthe slots adjacent the other end portion I5. Closer spacing of the slotswill increase the electrical resistance of the grid portions denedthereby and thus will increase the temperature of the electric iron insuch regions, If it is desired to manufacture a heating element adaptedfor use in an appliance other than an electric iron, the slots may beformed to dei-lne any desired shape of heating element, as will becomeclearly apparent from the yfollowing description. For the purpose ofsupporting and aligning the element with the die during successivestages of the manufacturing operations, I may provide holes or openingsI5 at the respective opposite ends of the plate I Ii for cooperatingwith suitable guide pins to accurately locate the plate duringsubsequent stamping operations. Where the slots are formed by a stampingoperation, the holes I5 may be formed in the same step as the slots.

In acordance with the invention, the slotted plate depicted in Figure 4may be formed either by a stamping operation or by an etching process.In a preferred embodiment of the invention, the slots are stamped in theplate by a single operation of my novel die which is described in detailhereinafter. However, the method of making a heating element inaccordance with the invention contemplates the formation of the slots inany suitable manner such as, for example, by punching out the slots oneat a time or in groups, or by utilizing the etching process now to bedescribed in connection with Figures 2 and 3.

In forming the slots by etching, the plate III is coated on one or bothsides thereof by a layer of masking material I9. A plurality of slits 2Ucorresponding, respectively, to the slots I I, I3 are formed in themasking layer in any suitable manner, as by scratching the masking layerwith a sharp instrument. The plate is then immersed in a bath of asuitable acid reagent which corrodes the unmasked portions of the plateforming the slots II and I 3. In order to carry out the etching in aquick and eiicient manner, it is preferred to make the resistance platethe anode in an etching solution which may be a strong mineral acid,such as sulphuric, nitric or hydrochloric acid of the desiredconcentration and to apply a 'voltage of 50-60 volts to the anode andcathode. I have found that in this manner a Nichroine plate having athickness of @,003 may be etched through in about 5 to 6 seconds.Instead ofproviding a continuous coating of the masking material on theresistance plate, it is also possible to apply the masking material inthe form of a waxy film having the desired configuration by means of aprinting or lithographic process which eliminates the necessity ofscratching in the slots by a separate operation. The masking material isthen removed leaving the plate in the condition shown by Figure 4.

The slotted plate of Figure 4, whether produced by etching or stamping,is then placed in a suitable die and a central channel 22, Figure 5, isformed therein, the longitudinal edges 23 of which define the respectiveinner edges of the grid-like resistance elements I2, Figure 6.Preferably, the edges 23 are formed along the extreme inner ends of theslots Il but some tolerance is permissible in the width of channel 22,the essential feature being that each slot I I communicates with thechannel 22 to prevent a short circuit being formed between adjacentsegments of the resistance grids. It will be observed that the slots andthe channel are shaped to form circular passages 2li constitutingopenings for receiving supporting bolts to secure the heating element inproper position with respect to the structure associated therewith. Theend of channel 22 may terminate at a short slot 25 at the tip portionIii to provide uniform thickness of the heating element in this region.

The structure of the grid-like resistance units I2 is then completed bycutting away portions 25 of the plate, thus defining the outer edges 21,Figure 6, of grid-like resistance structures I2, The edges 2'! arepreferably formed along the extreme outer ends of slots I3 but mayextend inwardly a short distance beyond such outer ends, the essentialfeature being that the slots I3 separate and prevent a short circuitbetween adjoining outer ends of the segments of gridlike resistanceelements i2. It will be observed that the ends I5 of resistance elementsI2 terminate in integral fiat plate-like portions 25, 29 constitutingterminals for the heater element, such terminals lying in thesame planeas resistance elements I2.

The structure shown in Figure 6 has sufficient mechanical strength andrigidity to prevent buckling and bending of the resistance segments intoshort circuiting contact with each other. This is due to the fact thatthe grid-like resistance element is interconnected at the end It!thereof by a plate portion 32 which serves to connect elements I2 inseries. 'Ihe mechanical strength and rigidity is also due to theinterconnection of terminal members 28 and 29 by plate portion 33. Itwill be undersoody however, that plate portion 33 forms a short circuitbetween `portions of the grid-like structure at this time means of alayer 36, Figures 8 and 11, of thermoplastic resin, such as a suitableVinyl resin. This may be accomplished by coating the mica surface with asuitable thermoplastic resin, such as vinylseal, placing the resistancegrid thereon and then applying heat and pressure to the said plate bymeans of a metal surface, such as steel, which is heated to atemperature of 180-220 C. Preferably, the application of heat andpressure stops short of the terminal regions of the plate, which areinitially integrally connected so that such regions are not bonded tothe insulating surface. This permits the terminal regions to be slightlylifted up so that the short portion S3 of the metal plate bridging theterminal portions may be cut out. Thereupon heat and pressure may beapplied to the entire surface of the resistance plate so that theterminal regions are also firmly bonded to the mica plate by the layer36. The

bonding material serves to afford sufficient strength and rigidity topreserve the flatness and configuration of the heater element, at leastuntil it is rigidly mounted in an iron or other electrical appliance.Once the element is mounted in this fashion, it is immaterial whetherthe bond between the heating element and insulating sheet persists orwhether the bonding material is decomposed during operation of the iron.

After the bonding has been completed, I fill the slots I I, I3 with asemi-refractory insulating compound or mass 3T, Figures 8 and 11, whichremains in position after assembly and at all times, positivelyinsulates adjoining segments of the resistance elements from each other.A

suitable compound for this purpose is an oxide paste prepared from arefractory metal oxide, such as aluminum, calcium, or magnesium oxide, aller such as water glass or uncalcined borax and water.

After the slots are filled, a second sheet 31a, Figure 9, of heatresistant insulating material, such as mica, is bonded or otherwisesuitably secured to the exposed surface of plate I0, this sccond sheethaving openings therein permitting access to the respective terminalportions 2S and 29.

Alternatively, the bonding operation may be performed at any stage ofthe process so long as the grid-like resistance elements areinterconnected before the bonding in such fashion that the structure hassufficient mechanical strength and rigidity to prevent buckling andcontact of adjacent resistance elements. After bonding, theinterconnecting portions are severed to define the heater element. Thus,for example, the plate I0 of Figure 2 may be coated, on one side only,with masking material after which the other side thereof may be bondedto insulating sheet 35, Figure '7. The masking material is then removedfrom the coated face to define the nished heater element of Figure '7after which the assembly is etched electrolytically, a potential beingapplied to a number of points at the same time. In this manner, theinterconnecting portions are severed or removed by the etching and thecomplete resistance element is formed in a single etching `operation.Thereupon the interspacesebetween the slots may be filled, as described,with an oxide paste and a second insulating sheet bonded to the exposedsurface of the metal plate to form a cornpleted heater element.

Accordingly, the completed resistance element comprises a metal plate ofresistance material I0 having grid-like resistance elements I2, I2defined therein by the slots II and I3, inner edges 23 and outer edges2. The elongated grid-like resistance elements I2 are connected inseries by plate portion 32 and terminate, respectively, in flat integralplate-like terminal portions 23, 29 which lie in the same plane asgrid-like resistance elements I2. The grid-like portions of the elementare bonded to heat resistant insulating sheet 35 to secure the desirablemechanical strength and rigidity, and the insulating compound 3'1 fillsthe slots II, I3 to effectively insulate the respective resistancesegments from each other. A second sheet of insulating material, such asmica, is applied or bonded to the exposed surface of the plate, thissecond sheet having openings 38 therein for effecting connection to theterminals 28 and 29. In its completed form, the heater element is ofuniform thickness throughout and free from bonds, folds, soldered orwelded joints. The insulating layers are likewise completely plane andof uniform thickness throughout so that they can be pressed against theplane heater' element substantially in the complete absence of anyinterposed or entrapped air spaces or films. This is of criticalimportance as even an air film or gap of 0.0001 may very appreciablyreduce the efliciency of heat transfer. In this manner, theconcentration of heat in definite regions, which is characteristic ofconventional wire or ribbon-wound heater elements, and the resultingpresence of hot spots is completely avoided.

Suitable dimensions for the component parts of the novel heating elementare a thickness of about 0.001 to 0.004 inch for the plate Iii and athickness of about 0.004 to 0.005 inch for the insulating sheets 35 andSla. I prefer to utilize about to 150 slots on each side of the channel22, the Width of the slots varying from about 0.002 to 0.01 inch and thelength thereof being determined by the particular zigzag pattern desiredfor the heater element. The width of the grid-like portions defined bythe slots may vary from about 3% to inch, this dimension being adjustedin accordance with the heating effect desired in particular regions.

A modified form of resistance element, which is suitable for use in ahot plate, is shown by Figure 10. lThis element is formed in accordancewith the principles of the present invention and comprises a plate I0 ofresistance metal having generally semicircular grid-like resistanceelements I connected, at one end, by a plate portion t2 and terminating,at the other end, in integral, flat terminal members cl3. The griddikeportions are bonded to a sheet :irl of heat resistant insulatingmaterial and, prior to the bonding operation, the terminals wereinterconnected by a metal plate portion giving suicient mechanicalstrength to prevent buckling, this interconnecting portion being severedafter the bonding step. The resistance elements are defined, as in thecase of the element shown in Figure '7, by slots 45, the inner edges I6of a channel Gi, and outer edges d8. The slots are filled by a suitableinsulating compound or paste thus insulating adjacent segments of thegrid-like resistance elements.

Referring now to Figures 1 and '7, an electric iron is shown embodyingthe heating element of the present invention. The heating clement ismounted between a pair of metal plates or bodies 50, 5I which are heldtogether by bolts 52 extending through the respective openings 2li inthe heating element and also carrying a handle E3.

In accordance with the invention, I provide 9 terminals of novelconstruction for making connection to the respective plate-like terminalportions 28 and 29, these terminals making an efficient electricalconnection to the plate portions 28 and 29 while permitting them toremain in the plane of the heater element.

Each terminal, as shown in detail in Figure 1l, may comprise a metalsleeve or container member 55 having a lower iianged portion resting oninsulating sheet 31a and disposed in a cavityT formed in the upper ironmember 5|. Sleeve member 55 may be insulated from metal plate 5| by abushing or grommet 56 which is lapped over the top of plate 5|. A solidbody or rod 5l of compressed, conductive, powdered material, such asgraphite, is disposed within the container member 55 and a portion ofthis material extends through the opening 38 into contact with the ilatterminal portion 28. In preparing the terminal rod, pure graphite powderof high electrical conductivity is glowed while in powder form andcompressed into desired cylindrical shape generally without any binder.The resulting pressed graphite body is characterized by high mechanicalstrength, is unaffected by elevated temperatures, and has someelasticity to apply resilient pressure to the resistance plate. Thecompressed body of powdered material or rod is forced into contact withthe terminal portion in any suitable manner, such for example, as by aset screw 58 which is disposed on interior threads located at the top ofsleeve member 55. The set screw 58 should be formed of material which isnon-oxidizing at moderately high temperatures, such as nickel, monelmetal, or silver plated brass.

The member 55 also carries external means for making electricalconnection through the sleeve and compressed conductive material 51 tothe flat terminal portion 28. This external means may comprise a pair ofnuts 59, 6 threaded to the exterior of the sleeve. The nut 59 may beforced into engagement with grommet 5S and the top of plate member 5| tohold the terminal rmly in assembled position thereon. The nut 60 may beutilized to hold a lead or conductor in contact with sleeve 55 and nut59 to afford an electrical connection to the terminal portion 28. lt isalso possible, of course, to clamp or otherwise attach a conventionalcontactor pin to the terminal which is adapted to cooperate with aconventional connector at the end of a flexible cord.

It will be apparent that the entire heating element, including thegrid-like resistance elements |2 and the terminal portions 28, 29- isheld in a perfectly flat position between the metal plates 5D, 5| andthe insulating sheets 35, 31a. Accordingly, the insulating sheets may begreatly reduced in thickness, as compared with prior art structures,thus reducing the operating temperature of the heater element anddecreasing the temperature differential between the heater element andthe body of the iron. As a result, the heater element is placed underthe protection of the body of the iron due to the intimate heat exchangerelation therebetween. Furthermore, the heating element is absolutelyplane, of uniform thickness throughout and free from bonds, folds,soldered or welded joints. The terminals, one of which is provided foreach terminal portion 28 and 29, cooperate with the associated structureto maintain a perfectly at position for the entire heating element andto afford an efficient electrical connection thereto.

'Another important aspect of this invention relates to a die for formingthe slotted plate shown in Figure 4 by a single punching operation andto a method for making such a die. The die is shown by Figures 12 to l5in which upper and lower rectangular frame members 65 and 56,respectively, are mounted on four posts or rods 6l disposed at therespective corners thereof, as by bolts 68. A stationary die assembly 69is fixedly secured to the frame 65 in any suitable manner, for example,by bolts '58.

A movable unit generally indicated at li is mounted for reciprocatoryvertical motion on the rods 6l and this movable unit is actuated by areciprocatory shaft l2 connected to any suitable power source, notshown. The movable unit comprises a support or frame 13 to which issecured a tool carrying assembly 1li, as by bolts 15. A guide or headerassembly 'l is carried by the movable unit but is adapted for limitedrelative movement with respect to the tool carrying assembly M. To thisend, the guide assembly and tool carrying assembly are interconnected bymembers l1, Figure 12, each having a circular opening 18 for receiving abolt 19 which is attached to guide assembly 15 and a slot 88 forreceiving a bolt 8| attached to tool-carrying assembly lli. Accordingly,it will be apparent that the guide member may slide along the posts 8l,moving relatively to the tool-carrying assembly a distance determined bythe length of slots 88.

The guide assembly is urged to a spaced position with respect to thetool-carrying assembly by a pair of compression springs which aremounted in suitable recesses provided in the aforesaid guide andtool-carrying assemblies.

The tool-carrying assembly, guide assembly, and stationary die assemblyare each adapted to receive a row of stacked metal plates and hold saidplates in their stacked position. To this end, each assembly comprises apair of end frame members 85 and lateral frame members 81, Figure 14.The inner surfaces of frame members 8l' are shaped to form longitudinalslots 88, respectively, which are adapted to receive complementary endportions of the aforesaid metal plates.

The tool-carrying assembly carries a row 98 oi metal plates, the guideassembly carries a row 9| of metal plates and the stationary dieassembly carries a row 92 of metal plates, each row being supported, asstated, by the longitudinal slots 88 in frame members 81. In accordancewith the invention, corresponding plates in each row are of identicalthickness and have accurately machined parallel sides. Aligned slots 93are formed in each set of corresponding plates, these slots conforming,in size and location, to the slots to be formed in metal plate i8,Figure 4. |That is to say, the slots in each assembly are divided intotwo rows, the slots in each row being in parallel staggered arrangementwith their ends defining the edges of the heating element to be formed,which, in the example shown, is an element adapted for use in anelectric iron. It will be noted that the plates are of progressivelydecreasing thickness progressing toward the tip of the heating elementdefined thereby.

The edges of each slot in the stationary die assembly may divergesomewhat progressing away from the top of the plates to define cuttingedges at the top of the plate and permit severed material to be readilyejected from the die.

Each of the slots in the tool-carrying assembly carries a cutting toolor knife 95, Figures 13 and 15, having a flanged end portion 99 and anangular cutting edge 91. The flanged portion is held between the framemember 13, Figure l5, and tool-carrying assembly 14 and the body of theknife extends through the adjacent slot in toolcarrying assembly 14 andinto the corresponding slot in guide assembly 16, the cutting edge beingclosely spaced from the lower end of such corresponding slot.

From the foregoing description, the operation of my novel die may bereadily understood by those skilled in the art. A thin metal plate,suoli as the plate l of Figure 4, is placed on the upper surface ofstationary die assembly 89. Thereupon, the movable unit 1l is loweredcausing the guide assembly to press against and hold the plate iniiattened position on the stationary die member. Upon continued movementof the unit 1I, the tool-carrying member moves downwardly7 intoengagement with the guide assembly, causing the respective cutting edgesof the knives to penetrate the plate l0 and move into the slots in thestationary die assembly. In this manner, the slots ll and I3, Figure 4,are formed in the plate by a single punching operation. When the movableunit is retracted, the parts return to the position shown by Figure l2and the guide assembly is urged to a position spaced from thetoolcarrying assembly by the springs Z55.

In order to insure that corresponding plates in the three die assembliesshall be of exactly the same thickness and that the slots therein shallbe in precise alignment, I form each set of corresponding plates, whichI refer to as a die element, in a single machining operation. In Figure16, I have shown a set of hardened plates 99, constituting a dieelement, in side-by-side position upon a hardened steel frame |00 whichis secured to the table of a milling or grinding machine, as by amagnetic tool holder or clamp. It will be noted that portions IUI havebeen cut from the sides of the plates, thus defining tongues |02 which tinto the grooves 88, Figure 14, on the respective die assemblies.

In the machining operation, the plates are formed to identical thicknessand transverse slots are formed across the set of plates while they arein the aforesaid side-by-side position. In this manner, I insure thatthe corresponding plates in each die assembly are of precisely uniformthickness and that the slots 93 therein are in exact alignment.

Preferably, and in accordance with the invention, one end of the plateutilized in the stationary die assembly is elevated while the slot 93 isbeing formed, Figure 17. This may be accomplished by placing a spacerE03, which may be about 0.003 inch in height, between one side of theplate and the table of the grinding machine. In this manner, the slotE04 in this plate is of progressively increasing depth and forms ashoulder or cutting edge at |05 against which the plate I0 is positionedafter the die is assembled.

Instead of using three plates in side-by-side position, as illustratedin Figures 16 and 1'1, I may utilize a single piece of metal IES, FigureI8, having weakened portions |01 along which the metal piece is severed,after the machining operation, to form a set of plates 99. The weakenedportions or grooves 01 are preferably formed before the plate |06 ishardened.

It will be understood that the sets of plates forming the respective dieelements are made separately and that a number of such sets are utilizedto form the completed die. In assembling the die, the plates areassembled into rows, with I2 the plates of each die element occupyingcorrespending positions in the rows. Thereupon, the rows of plates areinserted into position in the slotted portions 88 of the respective dieassemblies and secured in position therein to form the completed die.

In some cases, where the die is used for cutting relatively thickmaterial, it may not be necessary to provide a guide assembly. In such astructure, each die element will consist of two plates, one for thestationary die assembly and the other for the tool carrying assembly.

While the present invention, as to its objects and advantages, has beendescribed herein as carried out in specic embodiments thereof, it is notdesired to be limited thereby but it is intended to cover the inventionbroadly within the spirit and scope of the appended claims. .Forexample, instead of concentrating the heat at the tip of the iron bydecreasing the width of the element adjacent the tip regions, it is alsowithin the scope of the invention to slightly roll down the tip portionof the heater element blank, thereby increasing the speciiic resistanceof the element in this region.

What is claimed is:

l. In a machine for forming a series of slots in a metal plate, astationary die assembly and a movable die assembly, each of saidassemblies comprising a row of stacked metal plates having parallelsides, corresponding plates in each row being of substantially identicalthickness and having aligned slots therein which are adapted to receivea cutting tool, the slots in each assembly being arranged in two rowswith staggered ends dening the outer and inner edges of a resistiveheating element, and a plurality of cutting tools mounted on saidmovable die assembly, each tool extending through a slot in the movabledie assembly and being adapted, during each stroke of the movable dieassembly, to pierce a plate mounted on the stationary die assembly andenter the corresponding slot in said stationary die assembly.

2. In a machine for forming a series of slots in a thin metal plate, astationary die assembly defining a plate supporting portion, a movableunit including a guide assembly and a tool carrying assembly adapted forrelative motion with respect to said guide assembly, each of saidassemblies comprising a row of stacked metal plates having accuratelymachined parallel sides, corresponding plates in each row being ofsubstantially indentical thickness and having slots therein which areadapted to receive a cutting tool, the slots in the guide assembly andtool carrying assembly being of equal depth throughout, the slots in thestationary die assembly being of increasing depth progressing away fromthe plate supporting portion thereof to define a cutting edge andfacilitate removal of severed pieces from the die, and means for urgingne guide assembly to a spaced position with respect to the tool carryingassembly.

3. In a machine for forming a series of slots in a thin metal plate, astationary die assembly, a movable unit including a guide assembly and atool carrying assembly adapted for relative motion with respect to saidguide assembly, each of said assemblies comprising a row of stackedmetal plates having accurately machined parallel sides, correspondingplates in each row being of substantially identical thickness and havinga set of aligned slots therein which are adapted to receive a cuttingtool, the slots in each assembly amasar.;

l being arranged in two rows Vwith staggered ends defining the outer andinner edges of a resistive heating element, and means for urging theguide assembly to a spaced position with respect t the tool carryingassembly.

4. In a machine for forming a series of slots in a thin metal plate, astationary die assembly, a movable unit including a guide assembly and atool carrying assembly adapted for relative motion with respect to saidguide assembly, each of said assemblies comprising a row or stackedmetal plates having accurately machined parallel sides, correspondingplates in each row being of substantially identical thickness and havinga set of aligned slots therein which are adapted to receive a cuttingtool, the slots in each assembly being arranged in two rows withstaggered ends defining the outer and inner edges ofa resistive heatingelement having a pointed tip, the thickness of the plates in eachassembly progressively decreasing as the tip portion is approached, andmeans for urging the guide asembly to a spaced position with respect tothe tool carrying assembly.

5. In a machine for forming a series of slots in a thin metal plate, astationary die assembly, a movable unit including a guide assembly and atool carrying assembly adapted for relative motion with respect to saidguide assembly, each or said assemblies comprising a row of stackedmetal plates having slots therein to receive and guide a cutting tool,corresponding plates in each row being of substantially identical sizeand shape with their slots in precise alignment, a plurality or" cuttingtools supported by said tool carrying assembly, each tool extendingthrough a slot in the tool carrying assembly and into the correspondingslot in said guide assembly, and means for urging said guide assembly toa spaced position with respect to said tool carrying assembly whereby,during each stroke of the movable unit, the guide assembly is adapted topress against a metal plate supported on said stationary die assembly,further movement of said unit causing each cutting tool to pierce theplate and enter the slot aligned therewith in the stationary dieassembly.

6. In a machine for forming a series of slots in a thin metal plate, astationary die assembly, a movable unit including a guide assembly and atool carrying assembly adapted for relative motion with respect to saidguide assembly, each of said assemblies comprising a row of/stackedmetal plates having accurately machined parallel sides, correspondingplates in each row being of substantially identical thickness and havinga set of aligned slots therein which are adapted to receive a cuttingtool, the slots in each assembly being arranged in two rows withstaggered ends dening the outer and inner edges of a resistive heatingelement having a pointed tip, the thickness of the plates in eachassembly progressively decreasing as to the tip portion is approached,and means for urging the guide assembly to a. spaced position withrespect to the tool carrying assembly, and a set of cutting tools on thetool carrying assembly, each tool extending through a slot in said toolcarrying assembly and into the corresponding slot in said guide assemblywhereby, during each stroke of the movable unit, the

guide assembly is adapted to press against a metal plate supported onsaid stationary die assembly, further movement of said unit causing eachcutting tool to pierce the plate and enterthe'slot aligned therewith inthe stationary die assembly.

7. In a machine for cutting a series of slots in a metal sheet or plate,the combination of a stationary die assembly having a plate supportingportion and a movable die assembly, each of the die assemblies includinga row of stacked metal plates with the opposite sides thereof mutuallyfacingeach other and corresponding plates in each row being ofsubstantially the same thickness and having substantially aligned slotstherein for receiving a cutting tool, the slots in the stationary dieassembly having widened clearance portions in the ends thereof remotefrom said plate supporting portion and the stacked plates in each dieassembly having the slots arranged in two rows with staggered endsdening the outer and inner edges of a resistance heating element; and aplurality of cutting tools mounted on said movable die assembly witheach cutting tool extending through a slot therein in effective positionto pierce a metal sheet or plate supported on the plate supportingportion of said stationary die assembly and enter the corresponding slotin said stationary die assembly during each cutting stroke of saidmovable die assembly.

8. In a machine for cutting a series of slots in a thin metal sheet orplate, the combination of a stationary die assembly defining a platesupporting portion; a movable unit comprising a guide assembly and atool carrying assembly mounted for relative movement with respect tosaid guide assembly, each of said assemblies comprising a row of stackedplates having accurately finished sides mutually facing each other, andcorresponding plates ineach row being of substantially the samethickness and having slots therein adapted to receive a cutting tool,the guide assembly and tool carrying assembly having the individualslots therein of equal depth throughout, and the stationary die assemblyhaving each slot therein progressively increasing in depth away from theplate supporting section thereof to dene a cutting edge and facilitateremoval of severed pieces from said stationary die assembly; and meansfor biasing the guidev assembly to a spaced apart position with respectto the tool carrying assembly.

9. In a machine for cutting a series of slots in a thin metal sheet orplate, the combination of a stationary die assembly defining a platesupporting portion; a movable unit comprising a guide assembly and atool carrying assembly mounted for relative movement with respect tosaid guide assembly, each of said assemblies lcomprising a row ofstacked plates having accurately finished sides mutually facing eachother, and corresponding plates in each row being of substantially thesame thickness and having a set of substantially aligned slots thereinadapted to receive a Cutting 13001, each assembly having the slotstherein arranged in two rows with staggered ends defining the outer andinner edges of a resistance heating element; and means for biasing theguide assembly to a spaced apart position with respect to the toolcarrying assembly.

10. In a machine for cutting a series of slots in a thin metal sheet orplate, the combination of a stationary die assembly dening a platesupporting portion; a movable unit comprising a guide assembly and atool carrying assembly mounted for relative movement with respect tosaidguide assembly, each of said assemblies comprising a row of stackedplates having accuratelyv mshed ,Sides mutually .facing each other, and,

corresponding plates in each row being of Substantially the samethickness and having a set of substantially aligned slots thereinadapted to receive a cutting tool, each assembly having the slots hereinarranged in two rows with staggered ends deiining the outer and inneredges of a resistance heating element having a substantially pointed tipportion, the slots in the stationary die assembly being tapered towardthe plate supporting portion and the thickness of the plates in eachassembly progressively decreasing in the direction approaching said tipportion; and means for biasing the guide assembly to a spaced apartposition with respect to the tool carrying assembly.

11. In a machine for cutting a series of slots in a thin metal sheet orplate, the combination o a stationary die assembly denning a platesupporting portion; a movable unit comprising a guide assembly and atool carrying assembly mounted for relative movement with respect tosaid guide assembly, each of said assemblies comprising a row of stackedplates having accurately finished sides mutually facing each other andcorresponding plates in each row being of substantially the samethickness and having slots therein for receiving and guiding a cuttingtool, corresponding plates in each row being of substantially equal sizeand shape with their slots in precise alignment; a plurality of cuttingtools Supported on said tool carrying assembly, each cutting toolextending through a slot in the tool carrying assembly and into thecorresponding slot in said die assembly; and means for biasing the dieassembly to a spaced apart position with respect to the tool carryingassembly whereby, during each cutting stroke of the movable unit, thedie assembly initially presses upon a metal sheet or plate to be cutwhen supported on said stationary die assembly, while further movementof said unit causes each cutting tool to pierce the latter metal plateand enter the slot aligned with the cutting tool in said stationary dieassembly.

l2. In a machine for cutting a seriesof slots ina metal sheet or plate,the combination of a stationary die assemblyhaving a plate supportingportion and a. movable die assembly,each of the die assemblies includinga row of stacked metal plates with the opposite sides thereof mutuallyfacing each other and corresponding plates in each row bei ing ofsubstantially the same thickness and having substantially aligned slotstherein individually aligned slots therein individually cut in one sideof each stacked plate for receiving a. cutting tool, the stacked platesin each die assembly hav- ,y

ing the slots therein arranged in at least one row with staggered endsdefining the opposite edges of a resistance heating element; and aplurality of cutting tools mounted on said movable die assembly witheach cutting tool extending through a slot therein in eiective positionto pierce a metal sheet or plate supported on the plate supportingportion of said stationary die assembly and enter the corresponding slotin said stationary die assembly during each cutting stroke of saidmovable die assembly.

13. In a machine for cutting a series of slots in a metal sheet orplate, the combination of a stationary die assembly having a platesupporting portion and a movable die assembly, each of the dieassemblies including a row of stacked metal plates with the oppositesides thereof mutually facing each other and corresponding plates ineach row being of substantially the same thickness and havingsubstantially aligned slots there- F 16 in individually cut in one sideof each stacked plate for receiving a cutting tool, the stacked platesin each die assembly having the slots therein arranged in two rows withstaggered ends dening the outer and inner edges of a resistance heatingelement having a substantially pointed tip portion, the slots in thestationary die assembly being narrowed toward the plate supportingportion thereof and the thickness of the stacked plates in both dieassemblies progressively decreasing in the direction approaching saidtip portion; and a plurality of cutting tools mounted on said movabledie assembly with each cutting tool extending through a slot therein ineffective position to pierce a metal sheet or plate supported on theplate supporting portion of said stationary die assembly and enter thecorresponding slot in said stationary die assembly during each cuttingstroke of said movable die assembly.

14. In a machine for cutting a series of slots in a metal sheet orplate, the combination of a stationary die assembly having a platesupporting portion and a movable die assembly, each of the dieassemblies including a row of stacked metal plates with the oppositesides thereof mutually facing each other and corresponding plates ineach row being of substantially the same thickness and havingsubstantially aligned shallow slots therein individually cut in one sideof each stacked plate for receiving a thin cutting tool, the stackedplates in each die assembly having the slots arranged in at least onerow with staggered ends defining the opposite edges of a resistanceheating element; and a plurality of thin cutting tools mounted on saidmovable die assembly with each cutting tool extending through a slottherein in effective position to pierce a metal sheet or plate supportedon the plate supporting portion of said stationary die assembly andenter the corresponding slot in said stationary die assembly during eachcutting stroke of said movable die assembly.

15. In a machine for cutting a series of slots in a metal sheet orplate, the combination of a stationary die assembly having a platesupporting portion and a movable die assembly, each of the dieassemblies including a row of stacked metal plates with the oppositesides thereof mutually facing each other and corresponding plates ineach row being of substantially the same thickness and havingsubstantially aligned shallow slots therein individually cut in one sideof each stacked plate for receiving a thin cutting tool, the stackedplates in each die assembly having the slots arranged in two rows withstaggered ends dening the outer and inner edges of a resistance heatingelement having a substantially pointed tip portion, the slots in thestationary assembly being tapered toward the plate supporting portionthereof and the thickness of the stacked plates in both die assembliesprogressively decreasing in the direction toward said tip portion; and aplurality of thin cutting tools mounted on said movable die assemblywith each cutting tool extending through a slot therein in efectiveposition to pierce a metal sheet or plate supported on the platesupporting portion of said stationary die assembly and enter thecorresponding slot in said stationary die assembly during each cuttingstroke of said movable die assembly.

16. In a machine for cutting a series of slots in a metal sheet orplate, the combination of a stationary die assembly having a platesupport- 17 ing .portion and a movable die assembly, each of the dieassemblies including a row of stacked metal plates with the oppositesides thereof mutually facing each other and corresponding plates ineach row being of substantially the same thickness and havingsubstantially aligned shallow slots therein cut from the sides thereoffor receiving a cutting tool, the stacked plates in each die assemblyhaving the slots therein arranged in at least one row with staggeredends dening the opposite edges of a resistance heating element; and aplurality of cutting tools mounted on said movable die assembly witheach cutting tool extending through a slot therein in effective positionto pierce a metal sheet or plate supported on the plate supportingportion of said stationary die assembly and enter the corresponding slotin said stationary die assembly during each cutting stroke of saidmovable die assembly.

JOHN GYURIS.

REFERENCES CITED The following references are of record in the le ofthis patent:

